Impact of solute-solute interactions on grain boundary segregation and cohesion in molybdenum

Understanding the interactions of solutes in a host material is a key factor for successful alloy design. In this work, we focus on the effect of C, B, O, Fe, and Hf interactions in Mo on grain boundary (GB) segregation and cohesion within an ab initio framework. We show that segregation energies reveal only a weak coverage dependence for the interstitial solutes while for substitutionals a pronounced minimum occurs at 1 ML coverage. For Fe, segregation energies remain negative up to very high coverages of up to 8 ML, which correspond to thick segregation films whose geometric structure and magnetic properties are explored. As a next step we evaluate the binding energy for different solute combinations and show that interactions are mainly repulsive at the GB, while strong attractive interactions occur in the bulk. Origins for this phenomena are discussed and cosegregation energies are extracted for different scenarios. The coverage dependence on cohesion is nearly linear for all investigated solutes and increases for all solutes except for O and Hf.